My guess is safety. The thousands of other planes in the sky can't all accommodate one doing something unique for a special occasion.

The regime that governs air travel to assure safety makes sure that no path crosses any other path in three dimensional space (except at airports). Deviating from that arrangement assumes a lot of extra risk, and is probably absolutely forbidden.

I had a conflict preventing me from going to the path of totality. As it is, this became the third significant partial eclipse I've seen in 5.5 years, and one more partial will occur in 2023.

I'm thinking about the 2019 eclipse in South America. Northern Chile is one of the sunniest places in the world (hence the observatories!). Totality will also pass just south of Buenos Aires.

I also, per my plan, decided to scan the classifieds for a solar telescope, figuring that a lot of surplus would hit the market after August 21. Without looking too hard, I got a $100 discount on a barely-used one. So I'll be looking at the un-eclipsed Sun a lot more in the future.

My guess is safety. The thousands of other planes in the sky can't all accommodate one doing something unique for a special occasion.

The regime that governs air travel to assure safety makes sure that no path crosses any other path in three dimensional space (except at airports). Deviating from that arrangement assumes a lot of extra risk, and is probably absolutely forbidden.

For me JRehling's point here makes the actually-chosen course more difficult to understand, not easier. Most of the Asia-West Coast trans-oceanic traffic in that area is bound to be east-west, very much like the eclipse path, and the safest parallel non-intersecting course would be to go with the flow as much as possible, first flying westward to meet the oncoming shadow, and then returning east while trying to keep pace with it. By contrast, the polygonal path actually flown doesn't look like a simple solution to anybody's air traffic concerns.

The earlier points made by Explorer 1 and Tom Tamlyn are pretty persuasive on their own. The umbral spot should move at varying speeds depending on the angle formed by the earth's surface and the Sun-Moon-Earth line. Where the two are closest to perpendicular, somewhere around the middle of the track, the spot should slow to a theoretical minimum of about one hour per time zone, which might be about twice the speed of a passenger jet. Elsewhere it will move faster.

The regime that governs air travel to assure safety makes sure that no path crosses any other path in three dimensional space (except at airports).

I don't think I follow what you're saying. Flights flying compass headings of 0 to 179 fly at odd multiples of 1000 feet MSL, headings 180 to 359 fly at even multiples. That insures minimum vertical separation. And then there are systems like TCAS to help planes avoid each other. I doubt if planning this eclipse flight was all that challenging from an ATC perspective.

FWIW, I saw a different commercial airliner fly almost across the sun west to east a minute or so before totality in Oregon but I doubt if any of the passengers could see very well on that heading. Nice for the pilots, though.

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Disclaimer: This post is based on public information only. Any opinions are my own.

From extreme western Idaho a plane was visible flying into the umbra. I caught this with a time lapse sequence - here are two frames, about 6 seconds apart, showing the contrail just before and just after second contact:

The earlier frame has the shorter exposure, yet the trail appears brighter in it, so it's clear that the contrail darkened substantially (my goal is to end up with a radiometrically calibrated time lapse).

With the sun in the SE at the time, the plane must've been flying roughly south to north. With an estimate of it's altitude there may be some hope in identifying the flight. But from the plane the sun would've been 45 degrees high and roughly 35 degrees to the right as viewed through the starboard windows. Probably a difficult observation with typical airline windows. But of course the darkening of the sky and landscape would've been obvious.

I'm sure there were more examples of this given how packed the US airspace is.

In west Kentucky, there were quite a few planes with contrails moving along the shadow path as totality approached. It was apparent that a number of flight paths were somewhat modified for the eclipse. A video capture just before totality:

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